Stable electroluminescent devices

ABSTRACT

An electroluminescent device comprising a transparent or translucent support, a transparent or translucent first electrode, a second conductive electrode and an electroluminescent phosphor layer sandwiched between the transparent or translucent first electrode and the second conductive electrode, wherein the first and second electrodes each comprises a polymer or copolymer of a 3,4-dialkoxythiophene, which may be the same or different, in which the two alkoxy groups may be the same or different or together represent an optionally substituted oxy-alkylene-oxy bridge; a display comprising the above-mentioned electroluminescent device; a lamp comprising the above-mentioned electroluminescent device; manufacturing processes for the above-mentioned electroluminescent devices; and the use of such devices for the integrated backlighting of static and dynamic posters and signage.

[0001] The application claims the benefit of U.S. ProvisionalApplication No. 60/294,325 filed May 30, 2001 and the benefit of U.S.Provisional Application No. 60/349,572 filed Jan. 18, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates to stable electroluminescentdevices.

BACKGROUND OF THE INVENTION

[0003] EP-A 440 957 discloses dispersions of polythiophenes, constructedfrom structural units of formula (I):

[0004] in which R¹ and R² independently of one another representhydrogen or a C1-C4 alkyl group or together form an optionallysubstituted C1-C4-alkylene residue, in the presence of polyanions.

[0005] EP-A-686 662 discloses mixtures of A) neutral polythiophenes withthe repeating structural unit of formula (I),

[0006] in which R¹ and R² independently of one another representhydrogen or a C1-C4 alkyl group or together represent an optionallysubstituted C1-C4 alkylene residue, preferably an optionally with alkylgroup substituted methylene, an optionally with C1-C12-alkyl or phenylgroup substituted 1,2-ethylene residue or a 1,2-cyclohexene residue, andB) a di- or polyhydroxy- and/or carboxy groups or amide or lactam groupcontaining organic compound; and conductive coatings therefrom which aretempered to increase their resistance preferably to <300 ohm/square.Furthermore, the potential use of such layers as electrodes inelectroluminescence devices is disclosed.

[0007] ORGACON™ EL film is a commercially available subbed polyethyleneterephthalate support coated on one side with a transparent layer ofelectrically conducting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) [PEDOT/PSS] produced by Agfa-Gevaert N.V. It is promotedin the current brochure for this product as a low cost alternative topolyethylene terephthalate film coated with a transparent coating ofindium tin oxide (ITO) for use in electroluminescent lamps. T. Cloots etal. in the extended abstracts of the 5th International Conference on theScience and Technology of Display Phosphors held at San Diego on Nov.8-10, 1999 disclosed a comparison of electroluminescent lamps in whichITO-PET supports have been replaced with ORGACON™ EL film. However,under simulated ageing conditions of 60° C. and 90% relative humidityelectroluminescent devices produced with ORGACON™ EL film (seeCOMPARATIVE EXAMPLES 3 and 4) exhibited markedly inferior lifetimecompared with electroluminescent devices produced with ITO-PET (seeCOMPARATIVE EXAMPLES 1 and 2).

ASPECTS OF THE INVENTION

[0008] It is therefore an aspect of the present invention to provide anelectroluminescent device which is more economical to produce andexhibits comparable half-life and emission performances to prior artelectroluminescent devices.

[0009] It is a further aspect of the present invention to provideelectroluminescent devices with electrodes producible from dispersions,solutions or pastes by standard coating techniques e.g. screen coating.

[0010] Further aspects and advantages of the invention will becomeapparent from the description hereinafter.

SUMMARY OF THE INVENTION

[0011] Standard electroluminescent devices consist of a transparentsupport, two electrodes one of which is transparent and isconventionally an indium tin oxide (ITO) layer and the other isconventionally a carbon or silver layer, a dielectric layer isoptionally provided adjacent to the non-transparent electrode layer andan electroluminescent phosphor layer is sandwiched between thetransparent electrode and the dielectric layer if present or directlybetween the transparent and non-transparent electrodes if no dielectriclayer is present. Surprisingly it has been found that despite the factthat replacement of either electrode with a layer comprising a polymeror copolymer of a 3,4-ethylenedioxythiophene resulted in a markeddeterioration in the emission half-life of the device, replacement ofboth electrodes with a layer comprising a polymer or copolymer of a(3,4-ethylenedioxythiophene), e.g. poly(3,4-ethylenedioxythiophene)(PEDOT), led to a performance comparable with a device with ITO- andcarbon-electrodes.

[0012] The present invention provides an electroluminescent devicecomprising a transparent or translucent support, a transparent ortranslucent first electrode, a second conductive electrode and anelectroluminescent phosphor layer sandwiched between the transparent ortranslucent first electrode and the second conductive electrode, whereinthe first and second electrodes each comprises a polymer or copolymer ofa 3,4-dialkoxythiophene, which may be the same or different, in whichthe two alkoxy groups may be the same or different or together representan optionally substituted oxy-alkylene-oxy bridge.

[0013] The present invention also provides a process for producing theabove-mentioned electroluminescent device comprising the steps of: (i)coating a transparent or translucent support with a solution, adispersion or a paste of a polymer or copolymer of a3,4-dialkoxythiophene to produce the transparent or translucent firstconductive layer; (ii) coating the first conductive layer with a layercomprising an electroluminescent phosphor; (iii) optionally coating thelayer comprising an electroluminescent phosphor with a dielectric layer;and (iv) coating the dielectric layer, if present, or said layercomprising the electroluminescent phosphor, if no dielectric layer ispresent, with a solution, dispersion or paste comprising a polymer orcopolymer of a (3,4-dialkoxythiophene) to produce the second conductivelayer, wherein the polymer or copolymer of the (3,4-dialkoxythiophene)in the solution, dispersion or paste used in step (i) may be the same ordifferent from the polymer or copolymer of the (3,4-dialkoxythiophene)used in the solution, dispersion or paste used in step (iv).

[0014] The present invention also provides a process for producing theabove-mentioned electroluminescent device comprising the steps of: (i)coating a support with a solution, dispersion or paste comprising apolymer or copolymer of a (3,4-dialkoxythiophene) to produce the secondconductive layer; (ii) optionally coating the second conductive layerwith a dielectric layer; (iii) coating the dielectric layer if present,or the second conductive layer, if no dielectric layer is present, witha layer comprising an electroluminescent phosphor; and (iv) coating thelayer comprising the electroluminescent phosphor with a transparentsolution, dispersion or paste comprising a polymer or copolymer of a(3,4-dialkoxythiophene) to produce the transparent or translucent firstconductive layer, wherein the polymer or copolymer of a(3,4-dialkoxythiophene) in the solution, dispersion or paste used instep (i) may be the same or different from the polymer or copolymer of a(3,4-dialkoxythiophene) in the transparent solution, dispersion or pasteused in step (iv).

[0015] The present invention also provides for the use of a transparentpaste comprising a polymer or copolymer of a (3,4-dialkoxythiophene), apolyacrylate thickener and a glycol derivative, and optionally asurfactant for producing an electrode of the above-mentionedelectroluminescent lamp.

[0016] The present invention also provides for the use of theabove-described electroluminescent device in illuminated posters andsignage.

[0017] Preferred embodiments are disclosed in the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION Definitions

[0018] The term alkoxy means all variants possible for each number ofcarbon atoms in the alkoxy group i.e. for three carbon atoms: n-propyland isopropyl; for four carbon atoms: n-butyl, isobutyl andtertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl,2,2-dimethylpropyl and 2-methyl-butyl etc.

[0019] The term oxyalkylenealkoxy means two oxygen atoms linked by analkylene group. An alkylene group is a substituted or unsubstitutedhydrocarbon group e.g. a —(CH₂)_(n)— group where n is an integer between1 and 4, which may be substituted with an alkoxy, aryloxy, alkyl, aryl,alkaryl, alkyloxyalkyl, alkyloxyalkaryl, alkyloxyaryl, hydroxy, carboxy,carboxyalkyl, carboxyamino, sulfo or alkylsulfo group.

[0020] The term derivatives as used in connection with a particularpolymer refers to variants thereof substituted with alkyl, alkoxy,alkyloxyalkyl, carboxy, alkylsulfonato and carboxy ester groups.

[0021] The term transparent as used in disclosing the present inventionmeans having the property of transmitting at least 70% of the incidentlight without diffusing it.

[0022] The term translucent as used in disclosing the present inventionmeans allowing the passage of light, yet diffusing it so as not torender bodies lying beyond clearly visible.

[0023] The term aqueous as used in disclosing the present inventionmeans water and mixtures of water with water-miscible organic solventssuch as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amylalcohol, octanol, cetyl alcohol etc.; glycols e.g. ethylene glycol;glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g.2-propanone and 2-butanone etc. in which at least 50% by volume of wateris present.

[0024] Coating is a process in which a continuous or a discontinuouslayer is formed and includes printing techniques such as screenprinting, offset printing and flexographic printing.

[0025] The term flexible as used in disclosing the present inventionmeans capable of following the curvature of a curved object such as adrum e.g. without being damaged.

[0026] The term busbar refers to a highly conducting generally metalparticle-containing electrode applied to at least part of the surface ofthe first transparent or translucent electrode and to at least part ofthe surface of the second conductive electrode.

[0027] The term Newtonian behaviour refers to a viscosity with no morethan 10% variation in the shear rate range 1 to 80 s⁻¹ measured withincreasing shear rate for concentrations in the medium concerned up to2% by weight in the absence of other ingredients.

[0028] The term non-Newtonian behaviour refers to a viscosity with morethan 10% variation in the shear rate range 1 to 80 s⁻¹ measured withincreasing shear rate for concentrations in the medium concerned below2% by weight and in the absence of other ingredients.

[0029] PEDOT as used in the present disclosure stands forpoly(3,4-ethylenedioxythiophene).

[0030] PSS as used in the present disclosure stands for poly(styrenesulfonic acid) or poly(styrene sulfonate).

[0031] The terms illuminated posters and signage as used in disclosingthe present invention may also incorporate animation i.e. making one ormore areas turn ON or OFF at designated intervals of time.

Electroluminescent Device

[0032] An electroluminescent device according to the present inventioncomprises a transparent or translucent support, a transparent ortranslucent first electrode, a second conductive electrode and anelectroluminescent phosphor layer sandwiched between the transparent ortranslucent first electrode and the second conductive electrode, whereinthe first and second electrodes each comprises a polymer or copolymer ofa (3,4-dialkoxythiophene), which may be the same or different, in whichthe two alkoxy groups may be the same or different or together representan optionally substituted oxy-alkylene-oxy bridge.

[0033] According to a first embodiment of the electroluminescent devicesaccording to the present invention a dielectric layer is includedbetween the phosphor layer and the second conductive electrode.

[0034] According to a second embodiment of the electroluminescent deviceof the present invention dielectric layers are provided between theelectroluminescent phosphor layer and the transparent or translucentfirst electrode and between the electroluminescent layer and the secondconductive electrode.

[0035] The electroluminescent phosphor layer is generally 5 to 40 μmthick.

[0036] The transparent or translucent first electrode can be provided bycoating a paste, a dispersion or a solution.

[0037] The conductive second electrode can also be provided by coating apaste, a dispersion or a solution.

Preparation Process for an Electroluminescent Device

[0038] The present invention provides a process for producing theelectroluminescent device according to the present invention comprisingthe steps of: (i) coating a transparent or translucent support with asolution, a dispersion or a paste of a polymer or copolymer of a3,4-dialkoxythiophene to produce the transparent or translucent firstconductive layer; (ii) coating the first conductive layer with a layercomprising an electroluminescent phosphor; (iii) optionally coating thelayer comprising an electroluminescent phosphor with a dielectric layer;and (iv) coating the dielectric layer, if present, or said layercomprising the electroluminescent phosphor, if no dielectric layer ispresent, with a solution, dispersion or paste comprising a polymer orcopolymer of a 3,4-dialkoxythiophene to produce the second conductivelayer, wherein the polymer or copolymer of the (3,4-dialkoxythiophene)in the solution, dispersion or paste used in step (i) may be the same ordifferent from the polymer or copolymer of the 3,4-dialkoxythiophene)used in the solution, dispersion or paste used in step (iv).

[0039] The present invention provides a second process for producing theelectroluminescent device according to the present invention comprisingthe steps of: (i) coating a support with a solution, dispersion or pastecomprising a polymer or copolymer of a (3,4-dialkoxythiophene) toproduce the second conductive layer; (ii) optionally coating the secondconductive layer with a dielectric layer; (iii) coating the dielectriclayer, if present, or the second conductive layer, if no dielectriclayer is present, with a layer comprising an electroluminescentphosphor; and (iv) coating the electroluminescent phosphor layer with atransparent solution, dispersion or paste comprising a polymer orcopolymer of a (3,4-dialkoxythiophene) to produce the transparent ortranslucent first conductive layer, wherein the polymer or copolymer ofa (3,4-dialkoxythiophene) in the solution, dispersion or paste used instep (i) may be the same or different from the polymer or copolymer of a(3,4-dialkoxythiophene) in the transparent solution, dispersion or pasteused in step (iv).

[0040] The first and second electrodes each comprise a polymer orcopolymer of a (3,4-dialkoxythiophene), which may be the same ordifferent, and may be printed or coated from a solution, a dispersion ora paste.

[0041] According to a first embodiment of a process for producing adevice according to the present invention, the first transparent ortranslucent electrode is coated or printed from an aqueous paste.

[0042] According to a second embodiment of a process for producing adevice according to the present invention, the second electrode iscoated or printed from an aqueous paste.

Polymer or Copolymer of a (3,4-dialkoxythiophene)

[0043] The first and second electrodes of the electroluminescent deviceaccording to the present invention contain a polymer or copolymer of a3,4-dialkoxythiophene having the formula

[0044] in which, each of R¹ and R² independently represents hydrogen ora C1-4 alkyl group or together represent an optionally substituted C1-4alkylene group or a cycloalkylene group.

[0045] According to a third embodiment of the electroluminescent deviceof the present invention, the first and second electrodes of theelectroluminescent device preferably contain a polymer or copolymer of a3,4-dialkoxythiophene in which the two alkoxy groups together representan optionally substituted oxy-alkylene-oxy bridge.

[0046] According to a fourth embodiment of the electroluminescent deviceof the present invention, the polymers or copolymers of a3,4-dialkoxy-thiophenes in which the two alkoxy groups togetherrepresent an optionally substituted oxy-alkylene-oxy bridge are selectedfrom the group consisting of: poly(3,4-methylenedioxythiophene),poly(3,4-methylenedioxythiophene) derivatives,poly(3,4-ethylenedioxythiophene), poly(3,4-ethylene-dioxythiophene)derivatives, poly(3,4-propylenedioxythiophene),poly(3,4-propylenedioxy-thiophene) derivatives,poly(3,4-butylene-dioxythiophene) and poly(3,4-butylenedioxythiophene)derivatives and copolymers thereof.

[0047] According to a fifth embodiment of the electroluminescent deviceof the present invention, the substituents for the oxy-alkylene-oxybridge are alkyl, alkoxy, alkyloxyalkyl, carboxy, alkylsulfonato andcarboxy ester groups.

[0048] According to a sixth embodiment of the electroluminescent deviceof the present invention, in the poly(3,4-dialkoxythiophenes) the twoalkoxy groups together represent an optionally substitutedoxy-alkylene-oxy bridge which is a 1,2-ethylene group, an optionallyalkyl-substituted methylene group, an optionally C1-C12 alkyl- orphenyl-substituted 1,2-ethylene group, a 1,3-propylene group or a1,2-cyclohexylene group.

[0049] Such polymers are disclosed in Handbook of Oligo- andPolythiophenes Edited by D. Fichou, Wiley-VCH, Weinheim (1999); by L.Groenendaal et al. in Advanced Materials, volume 12, pages 481-494(2000); L. J. Kloeppner et al. in Polymer Preprints, volume 40(2), page792 (1999); P. Schottland et al. in Synthetic Metals, volume 101, pages7-8 (1999); and D. M. Welsh et al. in Polymer Preprints, volume 38(2),page 320 (1997).

Polyanion Compound

[0050] The polyanion compounds for use in the first and secondconductive electrodes of the electroluminescent device of the presentinvention are disclosed in EP-A 440 957 and include polymeric carboxylicacids, e.g. polyacrylic acids, polymethacrylic acids, or polymaleicacids and polysulphonic acids, e.g. poly(styrene sulphonic acid). Thesepolycarboxylic acids and polysulphonic acids can also be copolymers ofvinylcarboxylic acids and vinylsulphonic acids with other polymerizablemonomers, e.g. acrylic acid esters, methacrylic acid esters and styrene.A particularly preferred polyanion compound for use in the first andsecond conductive electrodes of the electroluminescent device accordingto the present invention is poly(styrene sulphonic acid) and copolymersthereof with styrene.

Paste Comprising a Polymer or Copolymer of a (3,4-dialkoxythiophene)

[0051] Suitable aqueous pastes comprising a polymer or copolymer of a(3,4-dialkoxythiophene) are disclosed in WO 99/34371 in which a screenpaste with a viscosity of 1 to 200 dPas is disclosed containing asolution or dispersion of a conductive polymer and optionally binders,thickeners and fillers. However, WO 99/34371 only specifically disclosesan acrylate binder with Newtonian behaviour.

[0052] It has been found that binders with non-Newtonian behaviour aresuitable thickeners for use in aqueous pastes or inks e.g. highmolecular weight homo- and copolymers of acrylic acid crosslinked with apolyalkenyl polyether, such as the CARBOPOL® resins of B. F. Goodriche.g. CARBOPOL® ETD 2623, and xanthan gum, e.g. BIOSAN® S from HerculesInc., USA and Kelzan® T from MERCK & Co., Kelco Division, USA. Thesebinders are particular types of the polyacrylate and polysaccharideclasses of binder. Polysaccharide thickeners include cellulose,cellulose derivatives e.g. carboxymethyl cellulose, guar gum and xanthangum.

[0053] Typically such pastes or inks have a pH of 2.0, because A. N.Aleshin et al. showed in 1998 in Synthetic Metals, volume 94, pages173-177, that pH's above 3 lead to a dramatic decrease in electricalconductivity. Furthermore, it has been found that the electricalconductivity of conductive layers produced with dispersions comprising apolymer or copolymer of a (3,4-dialkoxythiophene) typically exhibit adramatic decrease in conductivity for dispersions with pH's above 3.

[0054] However, it has been found that pastes or inks having a pH of upto 7 produced with a polymer or copolymer of a (3,4-dialkoxythiophene)and non-Newtonian binders of the type CARBOPOL, which require a pH of ≧4in order to obtain their maximum thickening effect in an aqueous medium;a glycol derivative; and optionally a surfactant can be used to producea transparent electrode for an electroluminescent lamp with a surfaceresistances≦1000 Ω/square at visual transmissions >75%. Such surfaceresistances are comparable with those typically observed for pasteshaving pH's≦3.

[0055] Suitable pastes can also incorporate binders with Newtonianbehaviour, pigments and dyes, crosslinking agents, anti-foaming agentsand surfactants.

[0056] Non-transparent pastes can, for example, be realized byincorporating a pigment such as LEVACRYL® A-SF, a black pigment fromBAYER, into the above-mentioned paste, used for producing transparentelectrodes, in a weight sufficient to give non-transparency in the layerthickness being coated. Other suitable black pigments are KL1925, acarbon black dispersion from DEGUSSA, and MHI Black 8102M, a carbonblack dispersion from MIKUNI, and titanium dioxide pigments.

[0057] Transparent coloured compositions can be realized byincorporating coloured dyes or pigments e.g. Rhodamine 6G, copperphthalocyanine and phthalocyanine pigments such as Flexonyl® Blau BZG, ablue-green pigment from BAYER.

[0058] Suitable cross-linking agents are epoxysilanes (e.g.3-glycidoxypropyltrimethoxysilane), hydrolysis products of silanes (e.g.hydrolysis products of tetraethyoxysilane or tetramethoxysilane) asdisclosed in EP 564 911, herein incorporated by reference, and di- oroligo-isocyanates optionally in blocked form.

[0059] A suitable anti-foaming agent is the silicone antifoam agentX50860A.

[0060] Preferred surfactants are anionic and non-ionic surfactants withnon-ionic surfactants being particularly preferred. Preferred non-ionicsurfactants are selected from the group of surfactants consisting ofethoxylated/fluroralkyl surfactants, polyethoxylated siliconesurfactants, polysiloxane/polyether surfactants, ammonium salts ofperfluro-alkylcarboxylic acids, polyethoxylated surfactants andfluorine-containing surfactants. Suitable non-ionic surfactants are:

[0061] Surfactant no. 01=ZONYL® FSN, a 40% by weight solution ofF(CF₂CF₂)1-9CH₂CH₂O(CH₂CH₂O)_(x)H in a 50% by weight solution ofisopropanol in water where x=0 to about 25, from DuPont;

[0062] Surfactant no. 02=ZONYL® FSN 100:F(CF₂CF₂)₁₋₉CH₂CH₂O(CH₂CH₂O)_(x)H where x=0 to about 25, from DuPont;

[0063] Surfactant no. 03=ZONYL® FS300, a 40% by weight aqueous solutionof a fluorinated surfactant, from DuPont;

[0064] Surfactant no. 04=ZONYL® FSO, a 50% by weight solution ofF(CF₂CF₂)₁₋₇CH₂CH₂O(CH₂CH₂O)_(y)H where y=0 to ca. 15 in a 50% by wt.solution of ethylene glycol in water, from DuPont;

[0065] Surfactant no. 05=ZONYL® FSO 100, a mixture of ethoxylatednon-ionic fluoro-surfactant with the formula:F(CF₂CF₂)₁₋₇CH₂CH₂O(CH₂CH₂O)_(y)H where y=0 to ca. 15, from DuPont;

[0066] Surfactant no. 06=TEGOGLIDE® 410, a polysiloxane-polymercopolymer surfactant, from Goldschmidt;

[0067] Surfactant no. 07=TEGOWET®, a polysiloxane-polyester copolymersurfactant, from Goldschmidt;

[0068] Surfactant no. 08=FLUORAD® FC431:CF₃(CF₂)₇SO₂(C₂H₅)N—CH₂CO—(OCH₂CH₂)_(n)OH from 3M;

[0069] Surfactant no. 09=FLUORAD® FC126, a mixture of the ammonium saltsof perfluorocarboxylic acids, from 3M;

[0070] Surfactant no. 10=Polyoxyethylene-10-lauryl ether

[0071] A particularly preferred non-ionic surfactant is ZONYL® FSO 100.Suitable anionic surfactants are:

[0072] Surfactant no. 11=ZONYL® 7950, a fluorinated surfactant, fromDuPont;

[0073] Surfactant no. 12=ZONYL® FSA, 25% by weight solution ofF(CF₂CF₂)₁₋₉CH₂CH₂SCH₂CH₂COOLi in a 50% by weight solution ofisopropanol in water, from DuPont;

[0074] Surfactant no. 13=ZONYL® FSE, a 14% by weight solution of[F(CF₂CF₂)₁₋₇CH₂CH₂O]_(x)P(O)(ONH₄)_(y) where x=1 or 2; y=2 or 1; andx+y=3 in a 70% by wt solution of ethylene glycol in water, from DuPont;

[0075] Surfactant no. 14=ZONYL® FSJ, a 40% by weight solution of a blendof F(CF₂CF₂)₁₋₇CH₂CH₂O]_(x)P(O)(ONH₄)_(y) where x=1 or 2; y=2 or 1; andx+y=3 with a hydrocarbon surfactant in 25% by weight solution ofisopropanol in water, from DuPont;

[0076] Surfactant no. 15=ZONYL® FSP, a 35% by weight solution of[F(CF₂CF₂)₁₋₇CH₂CH₂O]_(x)P(O)(ONH₄)_(y) where x=1 or 2; y=2 or 1 andx+y=3 in 69.2% by weight solution of isopropanol in water, from DuPont;

[0077] Surfactant no. 16=ZONYL® UR:[F(CF₂CF₂)₁₋₇CH₂CH₂O]_(x)P(O)(OH)_(y) where x=1 or 2; y=2 or 1 andx+y=3, from DuPont;

[0078] Surfactant no. 17=ZONYL® TBS: a 33% by weight solution ofF(CF₂CF₂)₃₋₈CH₂CH₂SO₃H in a 4.5% by weight solution of acetic acid inwater, from DuPont;

[0079] Surfactant no. 18=Ammonium salt of perfluoro-octanoic acid;

[0080] Layers of the pastes exhibit excellent adhesion to phosphorlayers, polyacrylate subbing layers, polycarbonate and polyesters e.g.poly(ethylene terephthalate) and surface resistances ≦1000 Ω/square atvisual light transmissions >75%, with ≧85% being obtainable.

[0081] Compositions of suitable pastes are given in Table 1. TABLE 1PEDOT PEDOT PEDOT paste paste paste 02 03 04 1.2% dispersion ofPEDOT/PSS [g] 100 100 100 CARBOPOL ™ ETD 2623 [g] 1.0 1.0 2.0 diethyleneglycol [g] 15 15 15 n-propanol [g] 10 10 10 LEVANYL ™ A-SF [g] — 3.61.92 ZONYL ™ FS100 [g] — — 0.16 ammonia (25% in water) to pH of 5 5 4.2

[0082] The compositions of prints printed with a manual press with P48mesh and P79 screens followed by drying at 110° C. for 5 minutes aregiven in Table 2 for PEDOT paste 02, 03 and 04. The surface resistancesof these prints were measured by contacting the printed layer withparallel copper electrodes each 35 mm long and 35 mm apart capable offorming line contacts, the electrodes being separated by a TEFLON®insulator. This enabled a direct measurement of the surface resistanceper square to be realized. The surface resistances are given in Table 2together with the optical densities of these layers measured intransmission with a MacBeth™ TR924 densitometer with a visible filter.In the case of the prints with PEDOT paste 02 the optical densitymeasurements were carried out on 10 strips and the optical densityobtained by the dividing the optical density obtained by ten aftersubtracting the optical density of the PET support. TABLE 2 PEDOT PEDOTpaste 02 paste 03 PEDOT paste 04 Screen P48 P79 P120 P48 P79 P48 P79P120 PEDOT/PSS [mg/m²] 455 285 — 443 277 443 277 — CARBOPOL ™ ETD 2623379 237 — 379 237 759 474 — [mg/m²] LEVANYL ™ A-SF [mg/m²] — — — 382 239204 127 — ZONYL ™ FS0100 [mg/m²] — — — — — 61 38 — surface resistance550 800 1600 — 700 600 830 1400 [Ω/square] optical density (vis) 0.080.06 0.03 — 0.50 0.80 0.58 0.44

Electroluminescent Phosphors

[0083] According to a seventh embodiment of the electroluminescentdevice of the present invention, the electroluminescent phosphor belongto the class of II-VI semiconductors e.g. ZnS, or are a combination ofgroup II elements with oxidic anions, the most common being silicates,phosphates, carbonates, germanates, stannates, borates, vanadates,tungstates and oxysulphates. Typical dopants are metals and all the rareearths e.g. Cu, Ag, Mn, Eu, Sm, Tb and Ce.

[0084] According to an eighth embodiment of the electroluminescentdevice of the present invention, the electroluminescent phosphor isencapsulated with a transparent barrier layer against moisture e.g.Al₂O₃ and AlN. Such phosphors are available from Sylvania, Shinetsupolymer KK, Durel, Acheson and Toshiba. An example of coatings with suchphosphors is 72×, available from Sylvania/GTE, and coatings disclosed inU.S. Pat. No. 4,855,189.

[0085] According to a ninth embodiment of the electroluminescent deviceof the present invention, the electroluminescent phosphor is ZnS dopedwith manganese, copper or terbium, CaGa₂S₄ doped with cerium,electroluminescent phosphor pastes supplied by DuPont e.g.: LUXPRINT®type 7138J, a white phosphor; LUXPRINT® type 7151J, a green-bluephosphor; and LUXPRINT® type 7174J, a yellow-green phosphor; andELECTRODAG® EL-035A supplied by Acheson. According to a tenth embodimentof the electroluminescent device of the resent invention, theelectroluminescent phosphor is a zinc sulphide phosphor doped withmanganese and encapsulated with AlN.

Dielectric Layer

[0086] Any dielectric material may be used in the dielectric layer, withyttria and barium titanate being preferred e.g. the barium titanatepaste LUXPRINT® type 7153E high K dielectric insulator supplied byDuPont and the barium titanate paste ELECTRODAG® EL-040 supplied byAcheson. A positive ion exchanger may be incorporated into thedielectric layer to capture any ions dissolving escaping from thephosphor of the light-emitting layer. The amount of ion exchanger in thedielectric layer has to be optimized so that it has a maximumeffectiveness in reducing black spots while not reducing the initialbrightness level. It is therefore preferred to add 0.5 to 50 parts byweight of ion exchanger to 100 parts by weight of the total amount ofresin and dielectric material in the dielectric layer. The ion exchangermay be organic or inorganic.

[0087] Suitable inorganic ion exchangers are hydrated antimony pentoxidepowder, titanium phosphate, salts of phosphoric acid and silicic acidand zeolite.

Transparent or Translucent Support

[0088] A transparent or translucent support suitable of use in theelectroluminescent device of the present invention may be rigid orflexible and consist of a glass, a glass-polymer laminate, a polymerlaminate, a thermoplastic polymer or a duroplastic polymer. Examples ofthin flexible supports are those made of a cellulose ester, cellulosetriacetate, polypropylene, polycarbonate or polyester, with polyethyleneterephthalate or polyethylene naphthalene-1,4-dicarboxylate beingparticularly preferred.

Uses of Electroluminescent Devices

[0089] The polymer thick-film electroluminescent devices according tothe present invention are particularly suitable for use in illuminatedposters and signage, particularly non-flat posters or signage or postersand signage subject to bending and flexing during use. Posters andsignage incorporating electroluminescent devices are commerciallyavailable with a 4-colour poster on one side of the support and anelectroluminescent device on the other are commercially available.However, such posters are produced by laminating the two devicestogether to the detriment of registration between the poster and theelectroluminescent device. Furthermore, the posters are produced byscreen printing with opaque inks and pastes, which results in relativelypoor resolution images and limited illumination possibilities.

[0090] The use of the electroluminescent device, according to thepresent invention, in association with flexible transparent supportsenables four colour printing techniques to be used with superior artworkand improved registration.

[0091] By incorporating animation i.e. making one or more areas turn ONor OFF at designated intervals, the attractiveness of the sign can begreatly enhanced in comparison to non-illuminated signs. The advantagesof such signs are: their thinness, their light weight, their flexibilityand their low power consumption.

Industrial application

[0092] An electroluminescent device according to the present inventioncan be used in lamps, displays, backlights e.g. LCD, automobiledashboard and keyswitch backlighting, emergency lighting, cellularphones, personal digital assistants, home electronics, indicator lampsand other applications in which light emission is required.Electroluminescent devices according to the present invention areoperated at an AC voltage of 30 to 3000V, typically 80 to 120V and afrequency of 50 to 10000 Hz, typically 400 to 1200 Hz.

[0093] The invention is illustrated hereinafter by way of COMPARATIVEEXAMPLES and INVENTION EXAMPLES. The percentages and ratios given inthese examples are by weight unless otherwise indicated. The lamps ofthe COMPARATIVE and INVENTION EXAMPLES illustrating the presentinvention used the supports given in Table 3. TABLE 3 subbing supportnr. polymer foil layer nr. coating 01* polyethylene terephthalate —sputtered ITO layer 02# polyethylene terephthalate 02 PEDOT/PSS layer 03polyethylene terephthalate 01 — 04 polyethylene terephthalate 02 — 05polyethylene terephthalate 03 — 06 polyethylene terephthalate 04 — 07**polyethylene terephthalate 05 — 08 polycarbonate 06 —

[0094] Subbing layer Nr. 01 (V671/02) has the composition: Copolymer of50 mol % ethylene glycol, 26.5 mol % 79.8% terephthalic acid, 20 mol %isophthalic acid, 3.5 mol % sulfoisophthalic acid Kieselsol 100 F, asilica from BAYER 19.9% ARKOPON ™ T, a surfactant from Clariant 0.3%

[0095] Subbing layer Nr. 02 (V664/14) has the composition: copolymer of88% vinylidene chloride, 10% methyl 79.1% acrylate and 2% itaconic acidKieselsol ® 100 F, a colloidal silica from BAYER 18.6% MERSOLAT ® H, asurfactant from BAYER 0.4% ULTRAVON ® W, a surfactant from Ciba-Geigy1.9%

[0096] Subbing layer Nr. 03 (V957/02) has the composition: copolymer of50 mol % ethylene glycol, 26.5 mol % terephthalic 77.2% acid, 20 mol %isophthalic acid, 3.45 mol % sulfoisophthalic acid and 0.05 mol % of

copolymer of 20% ethyl acrylate and 80% methacrylic acid  5.8%HORDAMER ® PE02, aqueous dispersion of polyethylene from  2.4% HoechstPAREZ RESIN ® 707, a melamine-formaldehyde resin from 14.6% AmericanCyanamid

[0097] Subbing layer Nr. 04 (T787) has the composition: Copolymer of 50mol % ethylene glycol, 26.5 mol % 79.8% terephthalic acid, 20 mol %isophthalic acid, 3.5 mol % sulfoisophthalic acid Kieselsol 100 F, acolloidal silica from BAYER 19.9% ARKOPON ® T, a surfactant fromClariant 0.3%

[0098] coated with: LAPONITE ® RD (magnesium silicate) 13.88% gelatin24.91% BRONIDOX ®, a bactericide 0.35% acylated ULTRAVON ® W, asurfactant from Ciba Geigy 1.42% ARKOPAL ® N60, a surfactant fromClariant 0.72% Trimethylolpropane 13.35% Kieselsol ® 500, a colloidalsilica from BAYER 41.63% PERAPRET ™ PE40, a polyethylene latex from BASF2.67% Poly(methyl methacrylate) matting agent 1.07%

[0099] The starting material for the preparation of the PEDOT pastesdescribed in the INVENTION EXAMPLES was a ca. 1.2% by weight aqueousdispersion of PEDOT/PSS containing a weight ratio PEDOT to PSS of 1:2.4prepared as disclosed in EP-A 440 957 and having a typical viscositymeasured using an AR1000 plate and cone rheometer (diameter 4 cm; coneangle 2°) at 20° C. of 38 mPa.s at a shear rate of 5 s⁻¹ decreasing to33.5 mPa.s at a shear rate of 35 mPa.s and has a typical pH of 1.9. Thisstarting material was either BAYTRON P from BAYER AG or was anAGFA-GEVAERT NV product.

INVENTION EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLES 1 TO 6 Preparationof PEDOT Paste 01

[0100] The PEDOT [poly(3,4-ethylenedioxythiophene)] paste 01 used forscreen printing the back electrodes on the dielectric layer of INVENTIONEXAMPLES 1 and 2 and COMPARATIVE EXAMPLES 5 and 6 was produced asfollows: a commercially available aqueous dispersion of PEDOT/PSS(BAYTRON® P from BAYER AG; weight ratio PEDOT:PSS=1:2.46) with 1.3% byweight solids was concentrated to a solids content of 3.0% by weight;and 160 g of this concentrate, 33.0 g of N-methylpyrrolidone, 4.8 g of3-glycidoxypropyltrimethoxy-silane, 15.3 g of a polyurethane dispersionand 87.0 g of dipropylene glycol dimethyl ether were stirred for 10minutes at 8000 rpm thereby obtaining PEDOT paste 01 with a viscosity ofca. 8 Pas at 25° C. and a shear rate of 10 s⁻¹.

Preparation of Electroluminescent Devices

[0101] The electroluminescent devices of INVENTION EXAMPLES 1 and 2 andCOMPARATIVE EXAMPLES 1 to 6 were prepared either using support 01 orsupport nr. 02 (see above) as follows:

[0102] screen printing the transparent electrode with a DuPont LUXPRINT®type 7151J electroluminescent phosphor paste;

[0103] then printing 2 or 3 layers of the DuPont LUXPRINT® type 7153Ehigh K dielectric insulator ink (barium titanate);

[0104] then printing a layer of the DuPont LUXPRINT® type 7144E, carbonconductor ink (resistance of 80 ohm/square), as the second electrode;and

[0105] finally applying a layer of the DuPont LUXPRINT® type 7145L rearelectrode, silver conductor (resistance of 1 ohm/square) or a layer ofPEDOT/PSS using PEDOT paste 01 (resistance of 1100 square).

[0106] Bus bars were applied to the transparent electrode with DuPontLUXPRINT® type 7145L rear electrode, silver conductor ink and to thesecond electrode if not silver. The configurations of theelectroluminescent devices of INVENTION EXAMPLES 1 and 2 and COMPARATIVEEXAMPLES 1 to 6 are given in Table 4. TABLE 4 support with firstinsulator second bus bar for 2nd electrode phosphor layers electrodeelectrode Comparative Example nr 1 nr. 01 (ITO) 7151J 3 of 7153J 7144E(carbon) 7145L ((silver) 2 nr. 01 (ITO) 7151J 3 of 7153J 7144E (carbon)7145L (silver) 3 nr. 02 7151J 2 of 7153J 7144E (carbon) 7145L (silver)(PEDOT/PSS) 4 nr. 02 7151J 3 of 7153J 7144E (carbon) 7145L (silver)(PEDOT/PSS) 5 nr. 01 (ITO) 7151J 2 of 7153J PEDOT paste 01 7145L(silver) 6 nr. 01 (ITO) 7151J 3 of 7153J PEDOT paste 01 7145L (silver)Invention Example nr 1 nr. 02 7151J 2 of 7153J PEDOT paste 01 7145L(silver) (PEDOT/ PSS) 2 nr. 02 7151J 3 of 7153J PEDOT paste 01 7145L(silver) (PEDOT/PSS)

[0107] Support nr. 02 (ORGACON® EL film) can be produced by conventionalcoating techniques and hence is much more economical to produce thansupport 02, ITO-60, produced by sputtering of indium tin oxide onpolyethylene terephthalate film.

Evaluation of the Electroluminescent Devices

[0108] The performance of the electroluminescent devices of INVENTIONEXAMPLES 1 and 2 and COMPARATIVE EXAMPLES 1 to 6 were evaluated insimulated endurance tests by monitoring the emission of the devices witha United Detector Technology Serial #67146 silicon photo-multiplier incontact with the non-coated side of the support when an AC voltage of100V at 400 Hz was applied to the electroluminescent devices in aconditioning chamber having a temperature of 60° C. and a relativehumidity of 90%. The initial emission in cd/m² and the emissionhalf-lives of the devices are given in Table 5. The percentage ofinitial resistance after 5 days was determined with a pair of devices,in which a voltage is only applied to one device and the resistance ofthe device to which a voltage had been applied monitored with respect tothe resistance of an identical device to which no voltage had beenapplied. The results expressed as a relative percentage with respect tothe device to which no voltage had been applied are given in the finalcolumn of Table 5. TABLE 5 Initial Emission % age of initial % age ofinitial emission half-life emission after resistance [cd/m²] [hours] 120hours after 120 hours Comparative Example nr 1 41 181 59 83 2 53 78 2186 3 38 16 0 644 4 33 20 0 653 5 43 10 0 136 6 36 10 0 151 InventionExample nr 1 35 83 37 129 2 29 89 38 187

[0109] The electroluminescent devices of COMPARATIVE EXAMPLES 1 and 2with a transparent electrode consisting of sputtered ITO and anon-transparent electrode of carbon have a configuration forelectroluminescent devices. It was surprisingly found that replacingeither the carbon electrode or the ITO-electrode in this conventionalconfiguration with a PEDOT/PSS-containing electrode resulted in asignificant deterioration in the lifetime of the electroluminescentdevice from >100 hours to 16 to 20 hours for replacement of theITO-electrode with a PEDOT/PSS-containing electrode, see the results forCOMPARATIVE EXAMPLES 3 and 4, and from >100 hours to 10 hours forreplacement of the carbon electrode with a PEDOT/PSS-containingelectrode, see the results for COMPARATIVE EXAMPLES 5 and 6.

[0110] It was therefore surprising that, despite the fact thatreplacement of either electrode in the conventional electroluminescentdevice configuration with a layer comprising a polymer or copolymer of a3,4-ethylenedioxythiophene resulted in a marked deterioration in theemission half-life of the device, replacement of both electrodes with alayer comprising a polymer or copolymer of a(3,4-ethylenedioxythiophene), e.g. PEDOT, led to a performancecomparable with a device with ITO- and carbon-electrodes.

[0111] From Table 5, it can be seen that the initial emission andhalf-lives of the lamps of COMPARATIVE EXAMPLES 1 and 2 in which the twoelectrodes were ITO and carbon were comparable to those of theelectroluminescent devices INVENTION EXAMPLES 1 and 2 in which the twoelectrodes contained PEDOT, according to the present invention.Moreover, ORGACON® EL film can be produced by conventional coatingprocesses and hence much more economically than ITO-60 sputter coatedfilm.

[0112] An important cause of failure of electroluminescent devices is anincrease in operating temperature due to heating of theelectroluminescent device as a result of electrical current transmissionthrough the device. This is equal to i²R and hence proportional to theresistance of the lamp. The increase in resistance during operation istherefore an indication of the operating temperature of theelectroluminescent devices and hence the potential lifetime of suchdevices in the absence of other failure mechanisms. The increase inresistance during operation was much lower for lamps with twoPEDOT-electrodes (see INVENTION EXAMPLES 1 and 2) than with lamps with aPEDOT-electrode and a carbon electrode (see COMPARATIVE EXAMPLES 3 and4) indicating a potentially longer lifetime for lamps with twoPEDOT-electrodes.

INVENTION EXAMPLES 3 TO 8 AND COMPARATIVE EXAMPLES 7 TO 12 Preparationof PEDOT Paste 02

[0113] PEDOT paste 02, a transparent PEDOT paste, was produced at 25° C.by carefully adding to 100 g of a 1.2% by weight dispersion of PEDOT/PSSin water at 800 rpm in a dissolver, 1 g of CARBOPOL® ETD-2623, 15 g ofdiethylene-glycol, 10 g of n-propanol and finally after 1 hour ofstirring the speed was increased to 1200 rpm and sufficient of a 25%solution of ammonia in water (ca. 0.5 ml) added to adjust the pH to avalue of 5 followed by stirring for a further 5 minutes.

[0114] The PEDOT paste 02 had a viscosity of 13 Pa.s at 25° C. and ashear rate of 10 s⁻. Screen printing with a P79 mesh followed by dryingat 110° C. for 5 minutes produced a layer with a surface resistance of800 Ω/square and an optical density of 0.06.

Preparation of PEDOT Paste 03

[0115] PEDOT paste 03, an opaque PEDOT paste, was produced at 25° C. bycarefully adding to 100 g of a 1.2% by weight dispersion of PEDOT/PSS inwater at 800 rpm in a dissolver, 1 g of CARBOPOL® ETD-2623, 15g ofdiethyleneglycol, 10 g of n-propanol, 3.6 g of LEVANYL™ A-SF, a blackpigment from BAYER, and finally after 1 hour of stirring the speed wasincreased to 1200 rpm and sufficient of a 25% solution of ammonia inwater (ca. 0.5 ml) added to adjust the pH to a value of 5 followed bystirring for a further 5 minutes.

[0116] The PEDOT paste 03 had a viscosity of 13 Pa.s at 25° C. and ashear rate of 10 s⁻¹. Screen printing with a P79 mesh followed by dryingat 130° C. for 2 minutes produced a layer with a surface resistance of700 Ω/square and an optical density of 0.50.

Preparation of Electroluminescent Devices

[0117] COMPARATIVE EXAMPLES 7 to 12 were prepared by screen printing thefollowing layer configuration through a P79 mesh screen onto support nrs3 to 8 (see above):

[0118] a layer of the DuPont LUXPRINT® type 7145L rear electrode, silverconductor (resistance of 1 ohm/square), was first applied forming abusbar for the first electrode;

[0119] a layer of paste 02 to a thickness after drying of 200 to 300 nmwas then applied thereby forming the first (transparent) electrode;

[0120] followed by a layer of LUXPRINT® 7151J, a zinc sulphide phosphordispersion from Dupont, to a thickness after drying of 20 μm;

[0121] then applying 3 layers of the DuPont LUXPRINT® type 7153E, high Kdielectric insulator ink (barium titanate), with drying between eachapplication each having a thickness after drying of ca. 7 μm;

[0122] then applying a layer of DuPont LUXPRINT® type 7144E ink, acarbon conductor ink (resistance of 80 ohm/square), to a thickness afterdrying of ca. 8 μm as a back electrode; and

[0123] finally a layer of the DuPont LUXPRINT® type 7145L rearelectrode, silver conductor (resistance of 1 ohm/square), oversufficient of the surface of the back conductive layer to form a bus barfor the rear electrode.

[0124] The layer configuration of INVENTION EXAMPLES 3 to 8 differedfrom that of COMPARATIVE EXAMPLES 7 to 12 only in the replacement of thelayer of DuPont LUXPRINT® type 7144E ink by a layer of PEDOT paste 03(surface resistance of 700 Ω/square) with a dry thickness of ca. 8 μm,which was dried at 120° C. for 2 minutes forming the secondPEDOT-containing electrode according to the present invention.

Evaluation of the Electroluminescent Devices

[0125] The results of a performance evaluation of the electroluminescentdevices of INVENTION EXAMPLES 3 to 8 and COMPARATIVE EXAMPLES 7 to 12 insimulated endurance tests as described for INVENTION EXAMPLES 1 and 2and COMPARATIVE EXAMPLES 7 to 12 are given in Table 6.

[0126] From Table 6, it can be seen that for lamps coated on the samesupport, the emission and half-life of the lamps of INVENTION EXAMPLES 3to 8 in which both the first and second electrodes were produced usingPEDOT pastes exhibited superior emission half-lives and percentages ofinitial emission after 5 days in simulated lifetime tests compared withthe lamps of COMPARATIVE EXAMPLES 7 to 12 in which the first electrodewas produced using PEDOT paste 02 and the second (back) electrode was acarbon electrode produced with DuPont LUXPRINT® type 7144E ink.Furthermore, a reduction in emission faults was also observed with thelamps of INVENTION EXAMPLES 3 to 8 compared with the emission of thelamps of COMPARATIVE EXAMPLES 7 to 12.

[0127] This improvement in emission half-life and percentage emissionafter 5 days in simulated lifetime tests was associated with a lowerincrease in lamp resistance over 120 hours of emission for all thesupports used.

[0128] Electroluminescent devices with two PEDOT-electrodes exhibitedsignificantly lower increases in lamp resistance compared with lampswith a single PEDOT-electrode when coated on the same support, whichindicated lower operating temperatures and hence potentially longer lamplifetimes in the absence of other failure mechanisms. TABLE 6 after 120h Initial Initial Emission Faults Faults % age of % age of supportemission resistance half-life after after initial initial nr. [cd/m²][Ω] [hours] 24 h? 192 h? emission resistance Comparative Example nr  703 34 914 67 none ca. 20% of 12 198.1 emitting area inactive  8 04 33840 36 none ca. 10% of 6 1561.9  emitting area inactive  9 05 32 776 28none point 6 759.0 faults 10 06 32 867 15 ca. 50% — 0 — emitting areainactive 11 07 30 802 33 none point 3 664.6 faults 12 08 29 896 74 point— 0 — faults Invention Example nr  3 03 29 774 70 none none 21 151.2  404 30 781 72 none none 20 212.3  5 05 29 736 60 none none 17 198.6  6 0628 844 70 inactive ca. 10% of 18 442.8 lines emitting area inactive  707 29 715 66 none point 17 175.8 faults  8 08 28 — 72 point point 11 —faults faults

[0129] This effect was particularly marked in the case of theelectroluminescent devices of COMPARATIVE EXAMPLE 8 with a singlePEDOT-electrode and INVENTION EXAMPLE 4 with two PEDOT-electrodes bothcoated on support nr. 04, in which in the case of the lamp ofCOMPARATIVE EXAMPLE 8 the lamp resistance had increased to 1562% of itsinitial value after emitting for 120 hours at 60° C. in a relativehumidity of 90% compared with 212% in the case of the lamp of INVENTIONEXAMPLE 4.

[0130] This shows the surprising benefit of using PEDOT-containing afirst transparent or translucent electrode together with a secondelectrode PEDOT-containing electrode, according to the presentinvention.

INVENTION EXAMPLES 9 to 14

[0131] INVENTION EXAMPLES 9 to 14 were prepared by screen printing thefollowing layer configuration through a P79 mesh screen onto support nrs3 to 8 (see above):

[0132] a layer of the DuPont LUXPRINT® type 7145L rear electrode, silverconductor (resistance of 1 ohm/square), was first applied forming abusbar for the “second” electrode;

[0133] a layer of PEDOT paste 03 was then applied to the silver-coatedsupport nrs. 3 to 8 to a thickness after drying at 130° C. for 2 minutesof 200 to 500 nm thereby forming the “second PEDOT-containing electrode”according to the present invention; then

[0134] 3 layers of the DuPont LUXPRINT® type 7153E, high K dielectricinsulator ink (barium titanate), were applied with drying between eachapplication each having a thickness after drying of ca. 7 μm;

[0135] then a layer of LUXPRINT® 7151J, a zinc sulphide phosphordispersion from Dupont, was applied to a thickness after drying of ca.10 μm;

[0136] a layer of PEDOT paste 02 (surface resistance of 800 Ω/square)was applied which upon drying at 90° C. had a thickness of ca. 8 μmforming the first PEDOT-containing electrode” according to the presentinvention and

[0137] finally a layer of the DuPont LUXPRINT® type 7145L rearelectrode, silver conductor (resistance of 1 ohm/square), to sufficientof the second electrode surface to form a bus bar therefor.

Evaluation of the Electroluminescent Devices

[0138] The performance of the electroluminescent devices of INVENTIONEXAMPLES 9 to 14 were evaluated in simulated endurance tests asdescribed for INVENTION EXAMPLES 1 and 2 and COMPARATIVE EXAMPLES 7 to12. The results are given in Table 7.

[0139] From Table 7, it can be seen that emission half-lives up to 51hours can be obtained with the so-called reverse lamp configurationdepending upon the support used, in which emission is observed throughthe uppermost layer rather than through the support as in theconventional electroluminescence lamp configuration, with aPEDOT-containing first transparent or translucent electrode togetherwith a second electrode PEDOT-containing electrode, according to thepresent invention. TABLE 7 after 120 h Invention Initial InitialEmission Faults % age of % age of Example support emission resistancehalf-life after faults after initial initial nr nr. [cd/m²] [Ω] [hours]24 h? 168 h? emission resistance 9 03 39 — 51 none inhomogeneous 10 —emitting area 10 04 37 — 39 none inhomogeneous 5 — emitting area 11 0539 — 32 point none 5 — faults 12 06 38 — 34 point none 5 — faults 13 0740 — 28 point none 2.5 — faults 14 08 42 — 26 none point faults 5 —

[0140] The present invention may include any feature or combination offeatures disclosed herein either implicitly or explicitly or anygeneralisation thereof irrespective of whether it relates to thepresently claimed invention. In view of the foregoing description itwill be evident to a person skilled in the art that variousmodifications may be made within the scope of the invention.

We claim:
 1. An electroluminescent device comprising a transparent ortranslucent support, a transparent or translucent first electrode, asecond conductive electrode and an electroluminescent phosphor layersandwiched between said transparent or translucent first electrode andsaid second conductive electrode, wherein said first and secondelectrodes each comprises a polymer or copolymer of a3,4-dialkoxythiophene, which may be the same or different, in which saidtwo alkoxy groups may be the same or different or together represent anoptionally substituted oxy-alkylene-oxy bridge.
 2. Device according toclaim 1, wherein said polymer or copolymer of a (3,4-dialkoxythiophene)is selected from the group consisting of:poly(3,4-methylenedioxythiophene), poly(3,4-methylenedioxythiophene)derivatives, poly(3,4-ethylenedioxythiophene),poly(3,4-ethylenedioxythiophene) derivatives,poly[3,4-(propylenedioxy)thiophene], poly[3,4-(propylenedioxy)thiophene]derivatives, poly(3,4-butylenedioxythiophene),poly(3,4-butylenedioxythiophene) derivatives and copolymers therewith.3. Device according to claim 1, wherein at least one of two saidelectrodes further comprises a polyanion compound.
 4. Device accordingto claim 3, wherein said polyanion compound is poly(styrene sulfonicacid).
 5. Device according to claim 1, wherein a dielectric layer isinserted between said phosphor layer and said second conductiveelectrode.
 6. A display comprising an electroluminescent devicecomprising a transparent or translucent support, a transparent ortranslucent first electrode, a second conductive electrode and anelectroluminescent phosphor layer sandwiched between said transparent ortranslucent first electrode and said second conductive electrode,wherein said first and second electrodes each comprises a polymer orcopolymer of a 3,4-dialkoxythiophene, which may be the same ordifferent, in which said two alkoxy groups may be the same or differentor together represent an optionally substituted oxy-alkylene-oxy bridge.7. A lamp comprising an electroluminescent device comprising atransparent or translucent support, a transparent or translucent firstelectrode, a second conductive electrode and an electroluminescentphosphor layer sandwiched between said transparent or translucent firstelectrode and said second conductive electrode, wherein said first andsecond electrodes each comprises a polymer or copolymer of a3,4-dialkoxythiophene, which may be the same or different, in which saidtwo alkoxy groups may be the same or different or together represent anoptionally substituted oxy-alkylene-oxy bridge.
 8. A process forproducing an electroluminescent device, comprising a transparent ortranslucent support, a transparent or translucent first electrode, asecond conductive electrode and an electroluminescent phosphor layersandwiched between said transparent or translucent first electrode andsaid second conductive electrode, wherein said first and secondelectrodes each comprises a polymer or copolymer of a3,4-dialkoxythiophene, which may be the same or different, in which saidtwo alkoxy groups may be the same or different or together represent anoptionally substituted oxy-alkylene-oxy bridge, comprising the steps of:(i) coating a transparent or translucent support with a solution, adispersion or a paste of a polymer or copolymer of a3,4-dialkoxythiophene to produce said transparent or translucent firstconductive layer; (ii) coating said first conductive layer with a layercomprising an electroluminescent phosphor; (iii) optionally coating saidlayer comprising an electroluminescent phosphor with a dielectric layer;and (iv) coating said dielectric layer if present, or said layercomprising the electroluminescent phosphor if no dielectric layer ispresent, with a solution, dispersion or paste comprising a polymer orcopolymer of a 3,4-dialkoxythiophene to produce said second conductivelayer, wherein said polymer or copolymer of said 3,4-dialkoxythiophenein the solution, dispersion or paste used in step (i) may be the same ordifferent from said polymer or copolymer of said 3,4-dialkoxythiopheneused in the solution, dispersion or paste used in step (iv).
 9. Processaccording to claim 8, wherein said paste is an aqueous paste. 10.Process according to claim 8, wherein said transparent solution ordispersion is an aqueous solution or dispersion.
 11. A process forproducing an electroluminescent device, comprising a transparent ortranslucent support, a transparent or translucent first electrode, asecond conductive electrode and an electroluminescent phosphor layersandwiched between said transparent or translucent first electrode andsaid second conductive electrode, wherein said first and secondelectrodes each comprises a polymer or copolymer of a3,4-dialkoxythiophene, which may be the same or different, in which saidtwo alkoxy groups may be the same or different or together represent anoptionally substituted oxy-alkylene-oxy bridge, comprising the steps of:(i) coating a support with a solution, dispersion or paste comprising apolymer or copolymer of a (3,4-dialkoxythiophene) to produce said secondconductive layer; (ii) optionally coating said second conductive layerwith a dielectric layer; (iii) coating said dielectric layer if present,or said second conductive layer if no dielectric layer is present, witha layer comprising an electroluminescent phosphor; and (iv) coating saidlayer comprising said electroluminescent phosphor with a transparentsolution, dispersion or paste comprising a polymer or copolymer of a(3,4-dialkoxythiophene) to produce said transparent or translucent firstconductive layer, wherein said polymer or copolymer of a(3,4-dialkoxythiophene) in said solution, dispersion or paste used instep (i) may be the same or different from said polymer or copolymer ofa (3,4-dialkoxythiophene) used in said transparent solution, dispersionor paste used in step (iv).
 12. Process according to claim 11, whereinsaid paste is an aqueous paste.
 13. Process according to claim 11,wherein said transparent paste is an aqueous transparent paste.
 14. Aprocess comprising the steps of: using a transparent paste comprising apolymer or copolymer of a 3,4-dialkoxythiophene, a polyacrylatethickener and a glycol derivative, and optionally a surfactant forproducing an electrode of an electroluminescent device comprising atransparent or translucent support, a transparent or translucent firstelectrode, a second conductive electrode and an electroluminescentphosphor layer sandwiched between said transparent or translucent firstelectrode and said second conductive electrode, wherein said first andsecond electrodes each comprises a polymer or copolymer of a3,4-dialkoxythiophene, which may be the same or different, in which saidtwo alkoxy groups may be the same or different or together represent anoptionally substituted oxy-alkylene-oxy bridge.
 15. A process comprisingthe steps of: using an electroluminescent device, comprising atransparent or translucent support, a transparent or translucent firstelectrode, a second conductive electrode and an electroluminescentphosphor layer sandwiched between said transparent or translucent firstelectrode and said second conductive electrode, wherein said first andsecond electrodes each comprises a polymer or copolymer of a3,4-dialkoxythiophene, which may be the same or different, in which saidtwo alkoxy groups may be the same or different or together represent anoptionally substituted oxy-alkylene-oxy bridge, in illuminated postersand signage.